Beware invaders – no matter how pretty!

MANY years ago, when my sister was a student, she and her five flat mates held a party.

It was all going well until someone they barely knew turned up in a glamorous outfit, flittered outrageously with every man in the place and drank all the booze – no one had invited her, she’d just been a brazen gatecrasher.

I was reminded of the incident a few days ago when I passed a hedgerow that was having the life squeezed out of it by another uninvited arrival.

This one was also tall and willowy and togged out in style, and it was also making itself at home where it wasn’t welcome.

Don’t be fooled by its good looks, Himalayan Balsam is a menace. This annual pink flower, introduced to the UK during the Victorian era, has spread itself around the country, choking the life out of our native vegetation.

It has made it on to the list of plants that are illegal to sell and if it is in your garden the best way to get rid of it is by pulling it up in early summer before it can flower and self-seed.

So what made this 10ft-tall plant with pretty pink flowers, so well-behaved on home soil, turn wild here?

The answer lies in our climate.

The UK is almost unique in being able to grow plants from around the world.

Species from South Africa, the Mediterranean, Asia and North America, all grow very happily at northern latitudes, thanks to the effect of the Gulf Stream.

A few love the conditions so much that, without extremes of temperature to keep them in check, they rapidly get out of control.

Some, like Himalayan Balsam, are very pretty. Others are striking or statuesque, but the reason why we need to keep these invaders at bay is they smother everything else.

The fact is, we have very few native species of our own.

Britain was still in the grip of the last ice age when it broke away from the continent, and as we began to warm up again, plants which had retreated were stopped from returning by the newly-opened English Channel.

It wasn’t until the Romans arrived, bringing vines and herbs, that our flora began to expand once more, and from the Middle Ages onwards, trade with Europe brought in exotic plants and bulbs.

It was in the 18th Century that plant-hunting started in earnest and from then on all kinds of new and exciting species started to arrive on these shores.

No one at the time could have predicted that the likes of Giant Hogweed or Rhododendron ponticum would turn feral once they got their roots into our soil.

I’ve seen streams in Argyll choked by American Skunk Cabbage and know of houses that have been made unsellable because of Japanese knotweed.

So if you see some pretty pink flowers growing among the brambles in a hedgerow, don’t be tempted to pick a few to take home.

You could be unleashing a monster.